Apparatuses and methods for voltage buffering

ABSTRACT

An apparatuses and methods for buffering a voltage from a circuit without current drive ability are described. An example apparatus includes a voltage buffer that includes two identical stages. The first stage is configured to receive an input voltage and produce an intermediate voltage as an output. The second stage is configured to receive the intermediate voltage and provide an output voltage that is equal to the input voltage. The voltage buffer may be coupled to a current source. The second stage of the voltage buffer may have current drive ability.

BACKGROUND

Memories and memory devices may include circuits that do not havecurrent drive ability. Voltages from these circuits may be provided toother circuits in the memories or memory devices. In some applications,the voltages may be used as reference voltages. For example, a band gapcircuit may provide a reference voltage to another circuit or a voltagemonitoring device. The reference voltage may vary if it is provided to acircuit that draws a current from the band gap circuit. The performanceof the circuit may degrade if the reference voltage varies. A voltagemonitoring device may receive an inaccurate measurement if the referencevoltage varies. It may be advantageous to prevent voltages provided bycircuits without current drive ability from varying when the voltagesare provided to other circuits or devices.

SUMMARY

An example apparatus according to the disclosure may include a currentsource that may be configured to provide a current, and a voltage buffercoupled to the current source to receive the current, wherein thevoltage buffer may include a first stage that may be configured toreceive an input voltage and provide an intermediate voltage, the firststage may be configured to receive the current from the current source;and a second stage may be configured to receive the intermediate voltageand provide an output voltage, the second stage may be configured toreceive the current from the current source.

An example apparatus according to the disclosure may include a firstload circuit, a second load circuit, a first transistor, wherein a drainof the first transistor is coupled to the first load circuit, a sourceof the first transistor is coupled to ground, and a gate of the firsttransistor may be configured to receive an input voltage, a secondtransistor, wherein a drain of the second transistor is coupled to thesecond load circuit, a source of the second transistor is coupled toground, and a gate of the second transistor is coupled to the source ofthe first load circuit and the drain of the first transistor, andwherein the drain of the second transistor may be configured to providean output voltage.

An example memory according the disclosure may include a pad, a testcircuit coupled to the pad and may be configured to provide an outputvoltage at the pad to be monitored, the test circuit and may include avoltage buffer that may be configured to receive an input voltage andprovide the output voltage, the voltage buffer may include: a firstactive load circuit, a second active load circuit, a first transistor,wherein a drain of the first transistor is coupled to the first loadcircuit, a source of the first transistor is coupled to ground, and agate of the first transistor may be configured to receive an inputvoltage, and a second transistor, wherein a drain of the secondtransistor is coupled to the second load circuit, a source of the secondtransistor is coupled to ground, and a gate of the second transistor iscoupled to the source of the first load circuit and the drain of thefirst transistor, wherein the first transistor, second transistor, andtransistors of the first and second active load circuits may be matched,and a current source coupled to the voltage buffer and may be configuredto provide a current to the voltage buffer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus according to an embodiment ofthe invention.

FIG. 2 is a circuit diagram of a voltage buffer according to anembodiment of the invention.

FIG. 3 is a block diagram of a test system according to an embodiment ofthe invention.

FIG. 4 is a block diagram of a portion of a memory according to anembodiment of the invention.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the disclosure. However, it will beclear to one having skill in the art that embodiments of the disclosuremay be practiced without these particular details. Moreover, theparticular embodiments of the present disclosure described herein areprovided by way of example and should not be used to limit the scope ofthe disclosure to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the disclosure. As used herein, apparatus may refer to, forexample, an integrated circuit, a memory device, a memory system, anelectronic device or system, a smart phone, a tablet, a computer, aserver, etc.

FIG. 1 is a block diagram of an apparatus 100 according to an embodimentof the invention. As used herein, apparatus may refer to, for example,an integrated circuit, a memory device, a memory system, an electronicdevice or system, a smart phone, a tablet, a computer, a server, etc.The apparatus includes a current source 105 coupled to a voltage buffer110. The current source may prevent excessive current consumption by thevoltage buffer circuit. The voltage buffer 110 may be configured toreceive an input voltage Vin. The input voltage Vin may be provided by acircuit with relatively weak current drive ability (not shown in FIG.1). The voltage buffer 110 may further be configured to receive acurrent Isrc from the current source 105. The voltage buffer 110 mayprovide an output voltage Vout, which may be equal to the input voltageVin. The output voltage Vout may be provided for use by another circuit,for example, the output voltage Vout may be monitored by a testingcircuit. The voltage buffer 110 may allow the input voltage Vin to beprovided to other circuits in the form of output voltage Vout withoutcurrent being drawn from the circuit from which the voltage buffer 110received the input voltage Vin. As a result, there may be lessvariability in the observed value of Vout.

FIG. 2 is a diagram of a circuit 200 according to an embodiment of theinvention. The circuit 200 includes a current source 205 and a voltagebuffer 210. The current source 205 and the voltage buffer 210 may beused for the current source 105 and the voltage buffer 110 previouslydescribed with and shown in FIG. 1. The current source 205 may be acurrent mirror, although other current sources may be used. The currentsource may include transistors 212, 215. The gates of the transistors212, 215 may be coupled to one another. The sources of transistors 212,215 may be coupled to a voltage source Vpp. Transistor 212 may have bothits drain and gate coupled to a resistance 213, which is in turn coupledto a voltage reference, for example, ground. The resistance 213 maylimit the current of the current source 205. Transistors 212, 215 may bep-channel transistors, but other transistor types may be used. Theresistance 213 may have a resistance value between 100 kΩ-1 MΩ. Othervalues of resistance may also be used without departing from the scopeof the disclosed invention. The drain of transistor 215 may be coupledto the voltage buffer 210 to provide a current Isrc.

The voltage buffer 210 may include two stages 240, 245. Transistors 220,230 may have their gates and drains coupled to the current source 205.The transistors 220 and 230 may be configured as load circuits thatprovide respective electrical loads to the stage 240 and the stage 245.In some embodiments, the transistors 220 and 230 may be configured asactive load circuits. The source of transistor 220 may be coupled to thedrain of transistor 225 and the gate of transistor 235. Transistor 225may receive input voltage Vin at its gate. The source of transistor 225may be coupled to a reference voltage, for example, ground. Transistor230 may have its source coupled to the drain of transistor 235. The gateof transistor 235 may be coupled to the source of transistor 220 and thedrain of transistor 225. The source of transistor 235 may be coupled toa reference voltage. An output voltage Vout may be provided from thesource of transistor 230 and the drain of transistor 235. Transistors220, 225, 230, 235 may be n-channel transistors, but other transistortypes may be used. In some embodiments, the transistors 220, 225, 230,235 may be matched. For example, transistors 220, 225, 230, 235 may allhave similar transistor dimensions and/or transistor characteristics. Insome embodiments, the matched transistors 220, 225, 230, 235 may beidentical, for example, the transistors 220, 225, 230, 235 may haveidentical transistor dimensions and/or identical transistorcharacteristics. Other transistor designs may also be used.

A voltage Vsupply may develop at the drains of transistors 220 and 230as a result of the current Isrc provided by the current source 205. Anintermediate voltage Vm may develop between stage 240 and stage 245 ofthe voltage buffer 210. The intermediate voltage Vm may be equal to thevoltage Vsupply minus the input voltage Vin. The output voltage Vout maybe equal to the voltage Vsupply minus the intermediate voltage Vm. Thus,the output voltage Vout may also equal the input voltage Vin. The stage245 may have current drive ability and provide Vout, but the voltagebuffer 210 prevents current being drawn from the source providing Vin atstage 240. This may allow for low mismatch and variation in the outputvoltage Vout. Circuits to which voltage Vout is provided may experienceless variable performance because of the voltage buffer 210.

A block diagram of an apparatus including a test system 300 that mayinclude an embodiment of the invention is illustrated in FIG. 3. Thetest system 300 may monitor multiple voltages V1-V4 from one or morecircuits (not shown). A multiplexer (MUX) 305 may be used to select avoltage from the multiple voltages V1-V4 to be provided as an inputvoltage Vin to the voltage buffer circuit 110. The MUX 305 may allowmultiple voltages to be monitored sequentially through a single voltagebuffer 110. The voltage buffer circuit 110 may provide an output voltageVout to a PAD 310 for monitoring by a monitoring device (not shown). Theoutput voltage Vout may be equal to the input voltage Vin. Accordingly,the monitoring device may monitor the value of the input voltage Vin bymonitoring the output voltage Vout. The monitoring device may measureless variation in Vout compared to existing monitoring circuits becauseno current is being drawn by the voltage probe or other monitoringdevice from the source providing Vin.

FIG. 4 illustrates a portion of a memory 400 according to an embodimentof the present invention. The memory 400 includes an array 402 of memorycells, which may be, for example, volatile memory cells (e.g., DRAMmemory cells, SRAM memory cells, etc.), non-volatile memory cells (e.g.,flash memory cells, PCM cells, etc.), or some other types of memorycells.

The memory 400 includes a command decoder 406 that receives memorycommands through a command bus 408 and generates corresponding controlsignals within the memory 400 to carry out various memory operations.The command decoder 406 responds to memory commands applied to thecommand bus 408 to perform various operations on the memory array 402.For example, the command decoder 406 is used to generate internalcontrol signals to read data from and write data to the memory array402. Row and column address signals are applied to the memory 400through an address bus 420 and provided to an address latch 410. Theaddress latch then outputs a separate column address and a separate rowaddress.

The row and column addresses are provided by the address latch 410 to arow address decoder 422 and a column address decoder 428, respectively.The column address decoder 428 selects bit lines extending through thearray 402 corresponding to respective column addresses. The row addressdecoder 422 is connected to word line driver 424 that activatesrespective rows of memory cells in the array 402 corresponding toreceived row addresses. The selected data line (e.g., a bit line or bitlines) corresponding to a received column address are coupled to aread/write circuitry 430 to provide read data to a data output buffer434 via an input-output data bus 440. Write data are applied to thememory array 402 through a data input buffer 444 and the memory arrayread/write circuitry 430.

Circuits according to an embodiment of the invention may be included inthe memory 400. For example, the circuit 200 (FIG. 2) may be included inthe data input buffer 444, which may include a bias voltage generator.The circuit 200 may be configured to operate as a voltage monitorcircuit used during testing of the memory device to confirm propergeneration of the bias voltage by the bias voltage generator within thedata input buffer 444. In some embodiments, test circuit 300 may beincluded in the memory 400, which may include multiple input bufferssimilar to input buffer 444. The MUX 305 may allow for the bias voltageof multiple input buffers to be monitored with the test circuit 300.Testing may be performed during manufacture of the memory or at a latertime.

Those of ordinary skill would further appreciate that the variousillustrative logical blocks, configurations, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer softwareexecuted by a processor, or combinations of both. Various illustrativecomponents, blocks, configurations, modules, circuits, and steps havebeen described above generally in terms of their functionality. Whethersuch functionality is implemented as hardware or processor executableinstructions depends on the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

The previous description of the disclosed embodiments is provided toenable a person skilled in the art to make or use the disclosedembodiments. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the principles defined hereinmay be applied to other embodiments without departing from the scope ofthe disclosure. Thus, the present disclosure is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope possible consistent with the principles and novel features asdefined by the following claims.

What is claimed is:
 1. An apparatus, comprising: a current sourceconfigured to provide a current; and a voltage buffer coupled to thecurrent source to receive the current, wherein the voltage bufferincludes: a first stage configured to receive an input voltage andprovide an intermediate voltage, the first stage configured to receivethe current from the current source; and a second stage configured toreceive the intermediate voltage and provide an output voltage, thesecond stage configured to receive the current from the current source.2. The apparatus of claim 1, wherein the first stage and the secondstage comprise matched transistors.
 3. The apparatus of claim 2, whereinthe matched transistors comprises n-channel transistors.
 4. Theapparatus of claim 1, wherein the current source is a current mirror. 5.The apparatus of claim 1, wherein the output voltage is equal to theinput voltage.
 6. The apparatus of claim 1, wherein the first stagecomprises a first load transistor and the second stage comprises asecond load transistor.
 7. The apparatus of claim 1, further comprisinga multiplexer coupled to the first stage, wherein the multiplexer isconfigured to receive a plurality of voltages and provide the inputvoltage to the first stage.
 8. An apparatus, comprising: a first loadcircuit; a second load circuit; a first transistor, wherein a drain ofthe first transistor is coupled to the first load circuit, a source ofthe first transistor is coupled to ground, and a gate of the firsttransistor is configured to receive an input voltage; a secondtransistor, wherein a drain of the second transistor is coupled to thesecond load circuit, a source of the second transistor is coupled toground, and a gate of the second transistor is coupled to the source ofthe first load circuit and the drain of the first transistor; andwherein the drain of the second transistor is configured to provide anoutput voltage.
 9. The apparatus of claim 8, wherein the first loadcircuit, second load circuit, first transistor, and second transistorare n-channel transistors.
 10. The apparatus of claim 9, wherein then-channel transistors have identical transistor characteristics.
 11. Theapparatus of claim 8, wherein the first load circuit comprises ann-channel transistor having a gate coupled to a drain and wherein thesecond load circuit comprises an n-channel transistor having a gatecoupled to a drain.
 12. The apparatus of claim 8, wherein the first loadcircuit and the second load circuit are configured to receive a current.13. The apparatus of claim 8, further comprising a current mirrorconfigured to provide a current to the first and second load circuits.14. The apparatus of claim 13, wherein the current mirror comprises twop-channel transistors.
 15. The apparatus of claim 13, wherein thecurrent mirror comprises a resistance coupled to a first p-channeltransistor and a reference voltage.
 16. A memory, comprising: a pad; atest circuit coupled to the pad and configured to provide an outputvoltage at the pad to be monitored, the test circuit including: avoltage buffer configured to receive an input voltage and provide theoutput voltage, the voltage buffer including: a first active loadcircuit; a second active load circuit; a first transistor, wherein adrain of the first transistor is coupled to the first load circuit, asource of the first transistor is coupled to ground, and a gate of thefirst transistor is configured to receive an input voltage; and a secondtransistor, wherein a drain of the second transistor is coupled to thesecond load circuit, a source of the second transistor is coupled toground, and a gate of the second transistor is coupled to the source ofthe first load circuit and the drain of the first transistor, whereinthe first transistor, second transistor, and transistors of the firstand second active load circuits are matched; and a current sourcecoupled to the voltage buffer and configured to provide a current to thevoltage buffer.
 17. The memory of claim 16, wherein the current sourcecomprises: first and second p-channel transistors having gates coupledtogether; and a resistance coupled to the first p-channel transistor.18. The memory of claim 16, wherein the test circuit further includes amultiplexer configured to receive a plurality of voltages, wherein themultiplexer is further configured to provide one of the plurality ofvoltages to the voltage buffer as the input voltage.
 19. The memory ofclaim 16, wherein the first and second load circuits of the voltagebuffer are coupled to the current source.
 20. The memory of claim 19,wherein the first transistor, second transistor, and transistors of thefirst and second active load circuits comprise matched n-channeltransistors.